The present invention relates to the art of presses and, more particularly, to a hydraulic fluid shock dampening system for a shearing press.
In a shearing press, as is well known, cooperable cutting die or shearing components are mounted on the press slide and bed to achieve cutting or shearing of material therebetween in response to movement of the press slide through the downward portion of its total stroke. Upon engagement of the die component on the slide with the material to be severed, a load is placed on the press which progressively increases to a maximum which is reached at the point of breakthrough of the shearing components with respect to the material therebetween. This load is imposed on the press through the slide, and movement of the slide toward the press bed is thus restrained during the severing operation. This restraint is removed upon breakthrough, whereupon slide movement toward the press bed is accelerated as a result of the load build up. In the absence of a restraining force with respect to such accelerated movement of the slide, shock loads including negative load forces are imposed on the press together with vibration forces, whereby unacceptable noise emanates from the press during operation thereof. It will be appreciated, of course, that these undesirable characteristics are repeated with each stroke of the press, and that shock loads and vibration are detrimental to press life as well as maintenance expenses in connection with component parts of the press. It will be further appreciated that high noise level is detrimental to the hearing of personnel working the press or working in the vicinity thereof. Vibration and high noise levels are also objectionable from the standpoint of other physiological effects on personnel, as well as psychological effects, and it is of course well known that these problems are of such a magnitude, and the potential detrimental effects thereof are of such concern, that government regulations have been established with respect to noise levels.
Many efforts have been made heretofore to dampen shock loads and vibrations in shearing presses, and in my U.S. Pat. No. 4,214,496, issued July 29, 1980, there is disclosed a hydraulic shock dampening system for shearing presses which provides a high degree of efficiency with regard to reducing shock load by eliminating negative load forces on the press upon material breakthrough. While such elimination of negative loading results in reducing shock loading and vibration, and thus advantageously promotes longer press life and lower maintenance costs, it has been found that the system vibrates at sonic frequencies following breakthrough, whereby the noise of operation while reduced is still undesirably high. In accordance with my earlier system, a flow sensitive valve having open and closed modes is in fluid flow communication with a hydraulic fluid receiving damping chamber interposed between the press slide and bed. The valve remains open and provides restricted fluid flow from the damping chamber at a fixed flow rate with minimal pressure drop during movement of the shearing component through the material being sheared and, at the point of breakthrough, acceleration of the slide quickly and positively shuts the valve to prevent any fluid flow from the chamber. Such stopping of flow from the damping chamber produces a rapid counterload against slide movement, thus reducing the energy release experienced at breakthrough. Accordingly, the load is maintained on the press through the slide following breakthrough, whereby negative loading of the press is eliminated and shock loading and vibration forces are reduced in comparison with other dampening systems. Initiating fluid flow across the valve prior to material breakthrough is important in that it establishes a directional flow of fluid through the system to avoid shock, vibration and resulting bouncing in the damping chamber and hydraulic system in response to the sudden closing of the flow sensitive valve and, more importantly, because it assures operation of the system immediately upon breakthrough. In this respect, it is the immediate response of the valve at the point of breakthrough and the sudden change from low pressure drop flow across the valve which provides the desired immediate counterload against slide movement and thus elimination of negative loads following breakthrough.